取代基效应对脂肪族链醚~(13)C NMR化学位移的影响

用原子电负性、极化度并结合表征原子空间连接方式的立体效应参数对醚分子中不同环境碳原子的化学位移进行关联,将23个脂肪醚中153个碳原子相关参数值和化学位移值带入模型中得到如下估算方程:δC=121.1348+94.3651Qi-2.0823QiΣαx-7.6347SH-47.6149SO(R=0.9990R2=0.9980S=0.85F=18478.97n=153)上式中Qi表示观测原子的部分净电荷,Σαx表示近邻原子极化度,SH,SO为立体效应参数.方程中各参数计算简单,物理意义比较明确,通过用"留一法"(LOO)检验(Rcv=0.9980,R2cv=0.9977,Scv=0.89)及对模型外4个化合物43个碳原子化学位移的预测值和实验值比较,结果表明模型具有较好的稳定性和预测精度.

Substituent Effects on 13 C NMR Chemieal Shift of Aliphatic Chain Ethers

The ¹³C NMR chemical shift for a given carbon atom in aliphatic ether molecules was related to the atomic electronegativity, polarizability and steric effects of the substituents. In this study, the relationship between ¹³C NMR chemical shift (δ_C) and the above parameters were established by multiple variable regression using 153 chemical shift values from 23 aliphatic ethers as the training set. The following formula was obtained: δ_C = 121.134 8+94.365 1Q_i-2.082 3Q_iΣα_x-7.634 7S_H-47.614 9S_O, where Q_i is the partial net charge on the given atom, Σα_x is the polarizability of the atoms near the given atom, S_H and S_O are the steric effect parameters. The stability and prediction capacity of the formula were tested using leave-one-out (LOO) cross-validation (cv) method (R_cv=0.998 0, R₂ cv=0.997 7 and S_cv=0.89), and confirmed by predictions of ¹³C NMR chemical shift of 43 different carbon atoms in 4 compounds.